Biometric sensors for verifying a user have been employed for decades in various areas. It is a well-known fact that certain biometric data is substantially unique to each person, which makes it a promising starting point for identifying such a person. Most notably, fingerprint sensors have been developed for the purpose of detecting a fingerprint and matching such a detected fingerprint with known data, but also voice recognition, retina scanning have been used. As an example, Precise Biometrics has a U.S. Pat. No. 6,241,288, which relates to an optical fingerprint identification/verification system using bitmaps of a stored fingerprint to correlate with a bitmap of an input fingerprint.
Various types of biometric sensors may be employed for giving access to information, or e.g. passage to secure areas, to trusted users only. Normally, such validation of a user is combined with other means for user identification, such as by showing proper printed identification credentials or the input of a code. One area of use for means for validating a trusted user is user input detection in electronic devices, such as mobile phones and computers. In such devices, it may be desirable to have some form of screen lock, for inhibiting access to certain information or making the device completely inoperable to anyone but a trusted user. On the other hand, such devices are normally frequently operated by the trusted user, and any type of unlocking feature should therefore not only be secure, but preferably also fast and simple. Fingerprint biometrics to logon to e.g. a mobile phone is becoming a de facto standard, and today there are devices on the market having a 3% False Rejection Rate (FRR), which means that 3 out of 100 times the system will reject a user when she tries to open the phone, even if she is the correct, trusted, user. Such a rejection, no matter how often it happens, is bad user experience.